<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>横切直角示例</title>
<style>
  .diagonal-cut {
    width: 200px;
    height: 200px;
    background-color: #3498db;
    clip-path: polygon(0 0, calc(100% - 20px) 0, 100% 20px, 100% 100%, 0 100%);
  }
</style>
</head>
<body>
 
<div class="diagonal-cut"></div>
 
</body>
</html>